Capacitor-based UPS

ABSTRACT

The present invention generally relates to the field of uninterruptable power supplies (UPSs) and more specifically, to UPSs using supercapacitors (also may be referred to as ultracapacitors) and/or other capacitor and/or battery elements. In an embodiment, a UPS of the present invention can individually regulate the charging of its capacitive elements to avoid overcharging and/or achieve a more efficient charge state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/658,098 filed on Jun. 11, 2012, U.S. ProvisionalPatent Application No. 61/696,363 filed on Sep. 4, 2012, and U.S.Provisional Patent Application No. 61/722,990 filed on Nov. 6, 2012, allof which is incorporated herein by reference in their entirety.

FIELD OF INVENTION

The present invention generally relates to the field of uninterruptablepower supplies (UPSs) and more specifically, to UPSs usingsupercapacitors (also may be referred to as ultracapacitors) and/orother capacitor and/or battery elements.

BACKGROUND

Uninterruptable power supplies (UPSs) have served the data center andthe industrial industry for many years. These UPSs are often implementedupstream of the network equipment, towards a facility's power entrance,and may be positioned in a centralized fashion to service an entire datacenter facility. Typically, 480 V (volt) AC (alternating current) isconverted to DC (direct current) where batteries are used to store theenergy. At a later time, the stored DC voltage is re-converted back toAC voltage for distribution throughout a facility. There is a trend inthe industry to distribute this UPS functionality down to the individualracks of a data center in an attempt to obtain improved energyefficiency. Other benefits of this distribution can include capitalsavings, improved scalability, and improved system reliability. However,at least one of the disadvantages of this technique is that batterypacks that are associated with individual racks often requiremaintenance as well as replacement after a relatively short lifetime.

Another trend in the industry is the replacement of traditionalbatteries with supercapacitors. These supercapacitors can have improvedlifetime as compared to common batteries (e.g., 5 times the lifetime ofa typical battery) and can result in improved performance versusbatteries in a distributed UPS architecture.

The combination of these two trends leads to the opportunity for thedevelopment of a supercapacitor-based UPS for use in facilities such asdata centers and industrial facilities.

SUMMARY

Accordingly, at least some embodiments of the present invention aregenerally directed to various capacitor-based UPSs and methods of usethereof.

In one embodiment, the present invention is a supercapacitor-based UPSsystem.

In another embodiment, the present invention is a module-basedbattery/capacitor unit.

In yet another embodiment, the present invention relates to chargingtechniques and methods.

In yet another embodiment, the present invention relates to redundancytechniques with a shared DC voltage bus across cabinets.

In yet another embodiment, the present invention relates to mountingoptions for a UPS and/or a UPS system.

In yet another embodiment, the present invention is a UPS comprising atleast one energy storage module having a plurality of capacitiveelements, input circuitry for providing electrical power from an inputto the at least one energy storage module, output circuit for providingelectrical power from the at least one energy storage module to anoutput, and charge-balancing circuitry. The charge-balancing circuitryat least partially retards charging of at least one the capacitiveelement when a voltage across the at least one the capacitive element isdetermine to be greater than a voltage across at least one other thecapacitive element by at least some first threshold amount, and thecharge-balancing circuitry resumes normal charging of the at least onethe capacitive element when the voltage across the at least one thecapacitive element is determined to be less than the voltage across theat least one other the capacitive element by at least some secondthreshold amount.

In yet another embodiment, the present invention is a UPS comprising atleast one energy storage module having a plurality of capacitiveelements, input circuitry for providing electrical power from an inputto the at least one energy storage module, output circuit for providingelectrical power from the at least one energy storage module to anoutput, communication circuitry providing a data communication link toan external managing device, and a microcontroller connected to thecommunication circuitry and the at least one energy storage module,where the microcontroller at least partially controls a maximum chargevoltage across at least one the capacitive element in response to aninput received from the communication circuitry.

In yet another embodiment, the present invention is a UPS comprising atleast one energy storage module having a plurality of capacitiveelements, input circuitry for providing electrical power from an inputto the at least one energy storage module, output circuit for providingelectrical power from the at least one energy storage module to anoutput, and capacity-measuring circuitry in communication with at leastone the capacitive element. The capacity-measuring circuitry measures afirst and a second voltage across the at least one the capacitiveelement, the measurement of the second voltage occurring at least sometime Δt after the measurement of the first voltage, and thecapacity-measuring circuitry provides an output based at least in parton the first voltage, the second voltage, and the Δt.

These and other features, aspects, and advantages of the presentinvention will become better-understood with reference to the followingdrawings, description, and any claims that may follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates typical discharge cycles of batteries and capacitors.

FIG. 2 illustrates series and parallel configurations for capacitors,and their associated energy capacities.

FIG. 3 illustrates a series/parallel supercapacitor configurationaccording to an embodiment of the present invention.

FIG. 4 illustrates a rack cabinet used together with a UPS according toan embodiment of the present invention.

FIGS. 5A and 5B illustrate various embodiments of the present inventionfor use in a data center.

FIG. 6 illustrates charging behavior of various capacitor systems.

FIG. 7 illustrates various embodiments of the present invention.

FIGS. 8A and 8B illustrate another embodiment of the present invention.

FIGS. 8C and 8D illustrate cell balancing in accordance with anembodiment of the present invention.

FIG. 8E illustrates a portion of a capacitor stack according to anembodiment of the present invention.

FIG. 9 illustrates a measurement technique according to an embodiment ofthe present invention.

FIG. 10A illustrates an embodiment of a UPS according to the presentinvention being used in an industrial setting.

FIG. 10B illustrates a block diagram of a UPS of FIG. 10A.

FIG. 11 illustrates a more detailed block diagram of a UPS of FIG. 10A.

FIGS. 12A and 12B illustrate an embodiment of a computer interface foruse with an embodiment of the present invention.

FIG. 13 illustrates a block diagram of an embodiment of the presentinvention.

DETAILED DESCRIPTION

Supercapacitors (also referred to as ultra-capacitors or EDLCs(electrochemical double-layer capacitors)) typically have capacitancevalues that are between 10,000 and 1,000,000 times larger thantraditional capacitors, making them good candidates for batteryreplacements. Some supercapacitors can have capacitances greater than6000 F (Farads) at a maximum voltage of about 3 V. The energy stored ina capacitor follows the equation: E=½ CV², where E is energy, C iscapacitance, and V is potential difference (voltage). Hence, asupercapacitor having capacitance of 6000 F at 3 V can store 27.0 kJ(kilojoules) (or 7.5 W-hr (watt hours)). This is comparable to theenergy stored in a standard D-cell sized battery. However, energyextraction from a capacitor is significantly different than that ofcommon batteries. This difference is illustrated in FIG. 1.

As illustrated in FIG. 1, with a constant current load, the batteryvoltage remains generally within an operating region until the maximumtime t_(max), where the battery can be considered discharged. For acapacitor, the voltage steadily declines until a minimum voltage isreached (at t=t_(max)) where the capacitor can be considered discharged.Note that with the capacitor-based system, when the capacitor voltagedrops below the minimum operating voltage (for example, 12 V), theoutput voltage must be “boosted” to maintain the output voltage neededto stay within the operating region. Also note that with acapacitor-based system, by measuring the capacitor voltage (and knowingthe capacitance), the energy capacity of the system may be calculated.With a battery-based system, an energy capacity measurement can be muchmore difficult to obtain.

Building a UPS system with the required amount of energy capacity canrequire that capacitors be assembled in series and/or in parallel. FIG.2 illustrates how the energy capacity of series (Case A) and parallel(Case B) capacitor circuits can be calculated. The examples of FIG. 2use capacitors measuring 2500 F (at 2.5V). The hold time for theseconfigurations with a 2 kW load is about 15.8 seconds. Note that astrictly parallel configuration may not be preferred because theregulator that follows the capacitor bank may need as much of a voltagerange as possible. For example, in Case A, if the voltage range spansfrom about 15V to about 1V, then more than 99% of the energy isutilized. However, in Case B, for a voltage range that spans from about2.5V to about 1V, only 84% is extracted. Hence higher voltages (withseries-connected capacitors) can be more efficient. Also note that thehold time of 15.8 seconds would probably not be appropriate for areal-world system, as the real-world hold time would preferably be inthe 4 to 5 minute range, requiring a larger system.

The capacitor configuration according to one embodiment of the presentinvention, as shown in FIG. 3, may be more appropriate for UPSapplications, as the voltage as well as the capacitance values areincreased (via parallelism). Combining the series groupings ofcapacitors into a module provides the ability to add versatility to aproduct manufactured in accordance with the present invention. Forexample, in one embodiment, one can add more modules 100 to a UPS 105 ifa longer hold time is required. In another embodiment, one can add moremodules 100 to a UPS 105 if a higher load needs to be sustained. In yetanother embodiment, older modules 100 can be replaced with newer modules100 having improved capacitance. In yet another embodiment, capacitorscan be combined with batteries.

In one embodiment of the present invention, the modules are designed toinclude at least one of the following functionalities: “hot-pluggable”(meaning the ability to slide modules in and out of the unit/systemwithout disrupting service); module scalability (modules can havedifferent capacity ratings); module identification (so the UPS canidentify the type and capacity of the modules that are plugged in); andthe use of a single value of module output voltage where a plurality ofmodules outputs a single voltage (for example, 12V). Thesefunctionalities may allow the UPS unit to use new, more advanced modulesas technology evolves, and may also allow battery-based modules to beused in combination with supercapacitor-based modules (and takeadvantage of newer battery technologies as they develop). In anotherembodiment, a UPS according to the present invention also has anadditional input/output DC power connection. This can allow more thanone unit to “share” the battery capacity across a number of cabinets.For example, if there are cabinets with low information technology(IT)-equipment loads, than by sharing the UPS capacity from those unitsto units that have a higher IT-equipment load it may be possible toallow the data center to sustain a more extended hold-time in the eventthat the data center has to rely on the UPS or the UPS system.

FIG. 4 illustrates an embodiment of the present invention, showing afront view and a rear view of a cabinet 110 with a UPS 105 mounted atthe bottom of the cabinet. The rear view shows the DC voltage cabling115 to the IT-Equipment 120 mounted within the cabinet 110 (in this casea plurality of servers). The DC cables 115 are fused at the back of theUPS 105 unit. Depending on the embodiment, physical placement of the UPS105 can be varied. For example, in one embodiment the UPS 105 can bemounted in the top section of the cabinet 110 above the IT-Equipment120. In other embodiments the UPS 105 can be mounted between theIT-Equipment 120. In yet other embodiment, the UPS 105 can be positionedseparate from the cabinet 110, including, but not limited to, on anoverhead tray, above panels of a ceiling, or underneath floor panels.Some of these embodiments are illustrated in FIGS. 5A and 5B.

Because supercapacitors can be damaged if their voltage exceeds thebreak down voltage, it is important to have a UPS or a system of linkedUPSs that can reduce or attempt to eliminate such occurrences. In oneembodiment of a UPS or a UPS system according to the present invention,where the UPS or the UPS system has a break down voltage (for example,about 3V), if one or more capacitors in a series stack is chargingfaster than the other capacitors (hence building up a voltage faster) orif all the capacitors are not exactly equal to one another, and one ormore capacitors exceeds a critical voltage (typically less than thebreak down voltage), then the charging of this particular capacitor isstopped while the other capacitors catch up. Illustrations of thedescribed behavior are illustrated in FIG. 6.

With reference to FIG. 6, in the “Ideal Case” when all the capacitorsC_(i) are exactly the same value, they will all charge together andtheir voltage will rise in the same manner. Monitoring the voltagesacross each capacitor C_(i) allows charging to be stopped when anycapacitor C_(i) reaches the critical voltage value (lower than thebreakdown voltage value). However, in the “Failure Case,” one of thecapacitors has a lower capacitance (e.g., C₃). In this case C₃ willcharge faster and could possibly exceed the critical voltage as well asthe breakdown voltage if the capacitor voltages are not monitoredindividually. One solution is to stop the charging whenever any of thecapacitor C_(i) voltages reaches a critical voltage. Another solutionwould be to stop charging the particular capacitor (or capacitors) C_(i)that have reached their individual critical voltage as shown in the“Preferred Case.” Yet another solution would be to keep the differencebetween the voltages of the individual capacitors C_(i) or groups ofcapacitors within a certain range during the charging cycle.

FIG. 7 describes some approaches to addressing the aforementionedcharging problem in accordance with some embodiments of the presentinvention. In the first (left) embodiment, zener diodes 125 are placedacross each of the capacitors C_(i) such that if any of the capacitorsexceed the zener voltage (set equal to the critical voltage) the voltageacross that capacitor C_(i) will be clamped and excess current willshunt around the capacitor C_(i) through the diode 125. In the second(right) embodiment, isolation switches 130 are added to isolateindividual capacitors C_(i) from the charging circuit. Once a capacitorC_(i) has been fully charged, the isolation switch(s) 130 disconnectthat capacitor C_(i) from the charging circuit.

Yet another embodiment is shown in FIG. 8A, where bleed resistors 135will shunt at least some of the current away from one or more of thecapacitors C_(i) if they are charging too fast. The bleed resistors areconnected to or disconnected from a charging capacitor C_(i) with aninline switch, and the capacitor voltages are individually monitored inorder to determine when to switch in the bleed resistors. Thecombination of a capacitor C_(i) and its respective switch and bleedresistor may be referred to as a cell, and the technique of using ableed resistor to shunt unnecessary current away from a capacitor may bereferred to as cell balancing. In one embodiment, the objective for cellbalancing is to attempt to ensure that all capacitors (regardless oftheir actual capacitance value) have a near-same voltage duringcharging. This can help ensure that no capacitor will inadvertentlyexceed its breakdown voltage and that a maximum charge will be storedacross the capacitor stack.

FIG. 8B generally describes the functionality of a single cell by way ofa non-limiting embodiment. During the charge interval of the capacitorsC_(i), the switches S_(i) are normally in the OPEN state. To determineif a particular switch or a series of switches need to be activated,voltages across each cell are monitored (generally monitored across arespective capacitor C_(i) and denoted v_(i) in FIG. 8B) and an averagecell voltage is determined. If the difference between any monitored cellvoltages and the average cell voltage reaches or exceeds a predeterminedSWITCH-ON threshold value (e.g., 30 mV (millivolts)), one or moreswitches S_(i) may be activated. For example, if the differenceindicates that monitored voltage of a particular cell is higher than theaverage cell voltage, the switch for that particular cell should beclosed (activated) and remain closed until the difference between themonitored cell voltage and the average cell voltage is equal to or lessthan a predetermined SWITCH-OFF threshold value (e.g., 10 mV).Conversely, if the difference indicates that the monitored voltage of aparticular cell is lower than the average cell voltage, the switches ofall remaining cells (all cells in a serial link excluding the particularcell) should be closed and remain closed until the difference betweenthe average cell voltage and the monitored voltage is again equal to orless than the predetermined SWITCH-OFF threshold value (e.g., 10 mV).

FIGS. 8C and 8D further exemplify cell balancing on a five-capacitorbank (also referred to as a stack) during a charge cycle. Each of thefive capacitors C_(i) has a corresponding voltage V_(i), where ‘i’corresponds to a respective capacitor. The values of the variousvoltages v_(i) are shown in the tables of FIGS. 8C and 8D, with eachtable having a series of columns representing the elapsed time inseconds from the start of a charge.

In FIG. 8C, for Case 1 where cell balancing is not used, the voltagevalues of each cell capacitor are derived for an example stack of 5capacitors with nominal capacitor values of 350 F (farads) except forthe particular cell capacitor of value 315 F (such variances may existdue to a variety of factors including, but not limited to, manufacturingtolerances and degradation of capacitors over time). The stack isassumed to be charging with a constant current of 1 amp. The result ofcell 5 having a lower capacitor value is that this cell charges fasterthat the remaining cells, and exceeds 3 volts at 960 seconds. Cell 5'svoltage is 305 mV larger than the remaining cell voltages. Assuming thatthe breakdown voltage for the each of the five capacitors is 3 volts,either of two situations can arise: i) cell 5 voltage can exceed thebreak down voltage or; ii) if the stack charging is terminated early toprevent cell 5 from exceeding its breakdown voltage, than the amount ofcharge stored in the remaining capacitors is less than what could beoptimally stored.

In Case 2 of FIG. 8C where cell balancing is utilized, at the end ofcharging, a more equal amount of voltage appears across all thecapacitor cells. Note that during the charging interval, for cell 5, atsome intervals cell balancing is turned on (as seen by the shaded boxes)and during other intervals it is turned back off. For example, at 95seconds the difference between the voltage of cell 5 and the averagevoltage of the remaining cells (represented by “delta V”) becomes equalto the SWITCH-ON threshold voltage (e.g., 30 mV). Since the voltage ofthe particular cell (in this case cell 5) is greater than the averagevoltage of the remaining cells, the switch for that particular cell isactivated, bleeding at least some current away from the C₅ capacitor andslowing its charge rate. This allows the remaining capacitors to catchup over time. Due to the slowed rate of charge, at 656 seconds thedifference between the voltage of cell 5 and the average voltage of theremaining cells becomes equal to the SWITCH-OFF threshold voltage (e.g.,10 mV) causing the switch of cell 5 to be deactivated. This processcontinues indefinitely to maintain a similar or approximately same rateof charge among all the capacitors of the stack.

In FIG. 8D, cell balancing is described for the case where a capacitorC₅ has a higher value than the nominal value of capacitors within thestack. For the case where cell balancing is not used (Case 1 of FIG.8D), at the time of 960 seconds, cell 5 (with the higher value ofcapacitance) has not charged up to the same value as the othercapacitors have charged to. Hence, there may be loss with respect toadditional opportunity of charge storage by not allowing cell 5 to fullycharge up such that the voltages would be approximately equal across allcapacitors of the stack. The use of cell balancing to achieve a moreeven charge is exemplified in Case 2. Note that in this case, since at115 seconds the difference between the voltage of the particular cell(in this case cell 5) becomes lower than the average voltage of theremaining cells by at least the SWITCH-ON threshold value, the switchesfor all the remaining cells are activated, thereby bleeding at leastsome current away from the respective capacitors and allowing theslower-charging capacitor C₅ to catch up. Once the difference betweenthe voltage of the particular cell and the average voltage of theremaining cells becomes equal to or less than the established SWITCH-OFFthreshold (which occurs at 660 seconds in the current example), theswitches of the remaining cells are deactivated resuming normalcharging. Similar to above, this process continues indefinitely tomaintain a similar or approximately same rate of charge among all thecapacitors of the stack.

Note that while the above embodiments have been described withparticular cell voltages being compared to all or remaining cell voltageaverages and determining whether a particular threshold has beenreached, other methods of determining a whether a certain cell is in orout of a threshold range are within the scope of the present invention.For example, one may compare the voltage of a particular cell to thevoltage of any other particular cell. In another embodiment, one maycompare the voltage of a particular cell to the highest/lowest voltagewithin a capacitor stack. In yet another embodiment, one may implementany combination of the aforementioned techniques.

An exemplary schematic for realizing an embodiment of a capacitor stackof the present invention utilizing bleed resistors is shown in FIG. 8E.In this schematic, C₁ is an ultra-capacitor (e.g., 350 F) which storesthe charge for Cell 12. Capacitor C₂ and resistor R₁ form an RC low passfilter to reduce noise in the cell's voltage measurement. Inductor L₁provides attenuation of any current transients arising from when theswitch closes or opens. M₁ is the cell's switch (e.g., a MOSFET) whichengages the bleed resistors (R₃ and R₄) to the ultra-capacitor to slowthe rate of charge. Resistor R₂ provides connection from amicroprocessor control output to the MOSFET switch's gate. It providesresistor isolation and protection for the gate of the MOSFET switch.Resistor R₃ and R₄ form the bleed resistor. They may be installed inparallel to increase the power rating. Diode D₁ provides the overvoltageprotection of the microcontroller's analog to digital convertor inputsand in case a cell capacitor is not present or open. The voltage monitorcan read the zener voltage (e.g., about 5 volts) if the ultra-capacitoris not present or opens.

As noted previously, with capacitor based system, in certain embodimentsit may be possible to determine the capacity of such a system. In orderto calculate the total amount of charge storage (Q=CV) within a stack ofcapacitors, the cell voltage and cell capacitance must be measured. Thecell voltage can be measured through an analog to digital voltageconvertor within the control circuitry and the capacitance can bemeasured by monitoring the cell voltage with the cell switch closedduring a finite time interval. An example of this measurement isillustrated in FIG. 9 where the capacitance is measured according to thefollowing:

$C_{measured} = {\left( \frac{\Delta\; t}{R_{i}} \right)*{\ln\left( \frac{V_{initial}}{V_{final}} \right)}}$

In this way the total charge stored across the capacitor stack C_(i) canbe determined. This information can be useful to calculate the real-time“hold-time” with a particular IT-Load and the operational lifetime ofthe UPS. As used herein, “real-time” can refer to instantaneous ornear-instantaneous.

Predicting the amount of hold-time in real-time may be a valuable assetto those who rely on UPS systems. Hold time is based on the energy thatis being drawn by the equipment and the amount of remaining energystorage within the ES modules. The amount of remaining energy in acapacitor-based storage element is predicted by the equation E=(½)CV².Hence, it is necessary to measure the capacitance. An accurate method tomeasure the capacitance is to load the capacitor bank and monitor thecurrent flow. The current (I) is related to the capacitance by I=CVΔt,where C is capacitance, and V is a potential difference, and Δt is timeperiod over which the current is monitored. Therefore, by monitoring thecurrent and voltage over a period of time (Δt) the capacitance can beaccurately measured. Thereafter, the capacitance and the energy draw canbe used to calculate the remaining hold time.

In another embodiment, a UPS or a UPS system of the present inventioncan be used in industrial settings such as industrial zone enclosures orindustrial control cabinets. FIG. 10A illustrates an embodiment where aUPS 105 of the present invention is used in an industrial application.In this embodiment, the UPS 105 is secured inside an industrial controlcabinet 140 and is connected to and/or mounted on a DIN rail 145. TheUPS 105 of FIG. 10A is small enough to fit inside the control cabinet,allowing the cabinet door to close when so desired. FIG. 10B illustratesa high-level block diagram of the UPS 105 of FIG. 10A, and FIG. 11illustrates a more detailed view of said UPS. The power supply 150converts the input AC voltage (e.g., 120 volts AC, 208 volts AC) into DCvoltage (e.g., 24 volts DC (VDC)). This 24 VDC is input into the UPSmodule. While FIG. 10B illustrates the power supply being separate fromthe UPS, other embodiments may incorporate the power supply into the UPSmodule. The output voltage of the UPS module is the protected andconditioned 24 VDC that is then applied to the electronic equipment.

In one embodiment, the UPS can perform power measurements at the input,output, and the energy storage module interface. This information cansubsequently be used to manage the UPS.

The UPS module also has an optional Ethernet LAN (local area network)interface, to report the status of various trackable variables as wellas to input policies into the module for application customization. Anexample of a computer interface from which the status of a UPS or a UPSsystem may be viewed and/or controlled from is shown in FIGS. 12A and12B. Other embodiments of the UPS may employ wireless and/or other meansof wired communication in place of an Ethernet LAN connection.

Additionally, the UPS module has an optional display which may be usedto display any particular trackable and/or computable variable, a seriesof variables, or any information related thereto. This display mayoutput the information either based on its pre-programmed parameters, orbased on a user's selection, where the user's selection may includedirecting the UPS to display a particular parameter or cycling through alist of parameters. The user's selection may be achieved by way of alocal input (e.g., an electric switch such as a button located on theUPS) or by way of a signal sent through a network interface such as anEthernet LAN.

Stored internally to the UPS are one or more energy storage (ES) modules100. These modules can be implemented in various technologies,including, but not limited to, ultra capacitors (such as those describedabove), lithium-ion, lead-acid, nickel-cadmium, and/or other batteryand/or capacitive elements. Such customization may allow a user greaterflexibility in finding a better match for the desired applications, aswell as retain a potential for future upgrades or other improvements.

A block diagram of a UPS in accordance with an embodiment of the presentinvention is shown in FIG. 13. In the illustrated embodiment, amicrocontroller 200 can act as the controller for the entire UPS unit.It can at least partially control at least one of the maintenance of theultra-capacitor stack (charging, discharging, capacitor measurements),the management interface to the outside network, status display LEDs,and voltage and the operation of the UPS itself (e.g., when to supplyexternal power to the IT-Equipment or to supply power via the capacitorstack). The UPS further includes an Ethernet to serial convertor 205.This converter provides an interface between a LAN (local area network)or a WAN (wide area network) connection and a serial connection to themicrocontroller 200. The information exchanged between a UPS-managingdevice such as a computer and the UPS passes through/resides with theEthernet to serial converter 205. The microcontroller 200 can read andwrite to this converter 205 to update information or get user controlinformation. The illustrated UPS further includes a hot-swap controller210 which has an input from an external 24 volt power supply anddelivers power to the output of the UPS as long as the external 24 voltpower supply is operational. The hot-swap controller 210 allows the UPSto remain operational when the external supply is changed to anotherpower supply or when the internal modules are replaced (hence the namehot-swap controller). The microcontroller 200 can further sense/monitorinput power current and voltage, and use that information to determinethe selection of the power supplies to connect to the output of the UPS.To maintain a reliable voltage supply for the UPS unit, a 24 VDC to 3.3VDC DC-DC converter 215 with diode “ored” inputs is utilized between theexternal supply and the capacitor stack. The 24 VDC to Stack Voltageblock 220 provides the charging circuitry for the ultra-capacitor stack227. Block 220 is linked to the output of the “Output Switching” block225 (which can be either power from the external supply or power fromthe ultra-capacitor stack), and also provides an output to the stack ofultra-capacitors 227. The Cell Balancing block 235 maintains thevoltages across the cells of the ultra-capacitor stack 227 such thatoptimal capacity is achieved. In the Stack Voltage to 24 VDC block 230the ultracapacitor stack voltage is converted from the stack voltage toa 24 VDC output. The stack voltage can be higher or lower than 24 VDC.At Output Switching 225 one of the voltage supplies is selected toconnect to the output voltage terminals. In the current embodiment, atemperature sensor 240 is connected to the microcontroller 200, whichcan be utilized to help maintain and/or manage the UPS. Additionally,LEDs 245 are connected to various components of the UPS to help providea visual indication of the status of at least some parts of the UPS.

Depending on the type of equipment that a UPS is attached to, theimportance of and the need for voltage conditioning may vary. In certainembodiments, the UPS of the present invention can be a multi-mode UPS.In such embodiments, the user can select whether the UPS operates in astatic way where it is manually adjusted to condition between the inputvoltage and the battery backup, or in a dynamic autonomous way where theconditioning is adjusted dynamically.

In other embodiments, the operation of a UPS or a UPS system of thepresent invention can be optimized for operating temperature andcapacity. Typically there is a tradeoff between the lifetime of anenergy storage element (such as a capacitor) and the energy storagecapability of the energy storage element (i.e., E=(½)CV²). Lifetime andcapacity are inversely related. Additionally, the operating temperatureof an energy storage element and its capacitance are also inverselyrelated. Therefore, one can optimize the energy storage system bymonitoring and/or tracking the capacitor temperature and adjusting thecapacitor voltage to maintain the preset desired lifetime (e.g., 10-15years). This may allow a user to run the energy storage elements such ascapacitors near their maximum voltage rating if the temperature is at alower level and still maintain a the desired ES module lifetime. If thesystem is experiencing higher operating temperatures, a user canmaintain the lifetime of the energy storage element by decreasing itsvoltage below its maximum voltage rating. However, a reduction of thevoltage at higher temperatures might correlate to a reduction incapacity at those temperatures. In this manner, a user can optimize thesystem based on lifetime and energy storage capacity requirements.

Note that the amount of voltage that the capacitors are charged to canbe controlled by the charging circuitry along with the cell balancingtechnique. If the objective of the present invention is to store morecharge, the voltage across the cell(s) can be increased. Such anincrease in voltage can result in an increase in hold-time, a lowertemperature tolerance, and/or a decrease in lifetime. If the objectiveof the present invention is to increase the lifetime of the UPS, thecell(s) can be charged to a lower voltage value. Such a lower charge canresult in a decrease in hold-time, a higher temperature tolerance,and/or a decrease in capacity. All these parameters can be controlled bythe voltage value on the cell capacitors.

Note that while this invention has been described in terms of one ormore embodiment(s), these embodiment(s) are non-limiting, and there arealterations, permutations, and equivalents, which fall within the scopeof this invention. It should also be noted that there are manyalternative ways of implementing the methods and apparatuses of thepresent invention. It is therefore intended that claims that may followbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

We claim:
 1. An uninterruptable power supply (UPS) comprising: at leastone energy storage module having a plurality of capacitive elementsconnected in series; input circuitry for providing electrical power froman input to the at least one energy storage module; output circuit forproviding electrical power from the at least one energy storage moduleto an output; and capacity-measuring circuitry in communication with theat least one capacitive element to: measure a first and a second voltageacross the plurality of capacitive elements, the measurement of thesecond voltage occurring at a time Δt after the measurement of the firstvoltage, measure a current through the plurality of capacitive elementsover the time Δt; calculate a capacitance of the plurality of capacitiveelements based on the measured first and second voltages and themeasured current; derive an amount of remaining energy in the at leastone energy storage module from the calculated capacitance; and output anestimated amount of real-time hold time remaining in the at least oneenergy storage module based on an amount of electrical power beingprovided on the output circuit from the at least one energy storagemodule and the derived amount of remaining energy in the at least onenergy storage module.
 2. The UPS of claim 1, wherein said at least onesaid capacitive element comprises an ultra-capacitor.
 3. The UPS ofclaim 1, wherein said at least one storage module is hot-swappable. 4.The UPS of claim 1 further comprising charge-balancing circuitry,wherein said charge-balancing circuitry at least partially retardscharging of said at least one said capacitive element when a voltageacross said at least one said capacitive element is determine to begreater than a voltage across at least one other said capacitive elementby at least some first threshold amount, and wherein saidcharge-balancing circuitry resumes normal charging of said at least onesaid capacitive element when said voltage across said at least one saidcapacitive element is determined to be less than said voltage acrosssaid at least one other said capacitive element by at least some secondthreshold amount.
 5. The UPS of claim 4, wherein said charge-balancingcircuit comprises a bleed resistor and a switch, said bleed resistorbeing connected in parallel with said at least one said capacitiveelement when said switch is activated.
 6. The UPS of claim 5, whereinsaid charge-balancing circuit further comprises an inductor connected inseries between said at least one said capacitive element and said bleedresistor.
 7. The UPS of claim 5, wherein said switch comprises a MOSFET.8. The UPS of claim 5 further comprising a microcontroller, saidmicrocontroller at least partially controlling a maximum charge voltageacross said at least one said capacitive element by at least one ofactivating and deactivating said switch.
 9. The UPS of claim 8 furthercomprising communication circuitry providing a data communication linkto an external managing device, wherein said microcontroller at leastpartially controls said maximum charge voltage across said at least onesaid capacitive element in response to an input received from saidcommunication circuitry.